One other thing I think they help with. Gettng a consistent arrow release from the string. No two nocks are identical, and if one is fitting tighter than the others, I think a string stop helps to make a cleaner release. A tight nock will travel further forwards with the string before it releases, but having a stop will make that a shorter distance.
2006 Rytera Bullet X 60#---2008 Moab 70#
2008/12 Firecat 60#--- 2010 Warthog 70#
2010/2012 Alien X 65# 2011 Onzas 60 & 70#
2009 Warthog 70#---2009 Firehawk 70#
2010 Strother SR-71 65# & 2012 Strother Rush 65#
I hunt, therefore I eat. lol